The consumption of non-sweetened and/or slightly sweetened breadmaking products is constantly on the increase. The production of these products uses breadmaking yeasts, termed baker's yeast, in dry, compressed or liquid form.
There are breadmaking yeast strains suitable for the various types of doughs: non-sweetened, slightly sweetened or strongly sweetened. Thus, the applicant proposes a complete range of yeasts intended for any type of breadmaking and for any baked bakery product.
However, yeast manufacturers are constantly in search of new yeast strains making it possible to produce yeasts which are even more effective, in particular in terms of fermentative capacities and of storage.
They are also constantly searching for an improved process for producing yeast, for instance improving production savings, which can be achieved by a higher productivity, by reducing production costs, by ease of implementation throughout the processes for producing yeast whatever the form: dry, compressed or liquid.
The robustness and regularity of the strain and also its resistance to drying are also properties that yeast manufacturers look for.
One of the reference strains of the applicant in this field is the one deposited on Feb. 12, 2003, with the CNCM (Collection Nationale de Cultures de Microorganismes [French National Collection of Microorganism Cultures], 26 rue du Docteur Roux, 75724 Paris cedex 15) under number I-2970. It is an important strain having multiple applications as dry yeast, as compressed yeast or as liquid yeast. Any improvement of this strain therefore has an impact on several products and qualities.
For a given strain and in light of the environmental conditions optimized in particular in terms of pH, of temperature, of fermentation medium, and of nitrogen (N) and phosphorus (P) resources, the most important parameter is the growth kinetics characterized by the evolution of the hourly multiplication rates and more globally the mean multiplication rate.
The mean multiplication rate is defined by
            (              Xend        /        X0            )        d    ,with                d=fermentation duration        Xend the amount of yeast at the end of fermentation        X0 the amount of yeast at the beginning of the fermentation.        
It is known that increasing the mean multiplication rate has the effect of increasing the fermentative capacity of a yeast to the detriment of a loss of productivity.
Indeed, under industrial fermentation conditions for producing baker's yeast, the growth rate is controlled by the sugar feed flow rate according to a fed-batch fermentation technology and under aerobic conditions, thereby making it possible to optimize both the biomass production yield and the fermented productivity.
The limits of the industrial process regarding the mean multiplication rate occur at several levels:
Over the course of the first third of the fermentation, the hourly multiplication rate is controlled so as to remain below the critical multiplication rate in order to avoid the respiro-fermentative metabolism associated with ethanol production which penalizes the yeast biomass production yield from the sugar.
Over the course of the rest of the fermentation, and as the yeast biomass increases in the fermenter, the hourly multiplication rate is gradually reduced so as to not be at the limit of the oxygen transfer capacity and cooling capacity of the industrial fermenter.
Overall, the higher the hourly multiplication rates, the more the metabolism makes it possible to obtain yeasts rich in proteins including the enzymes which confer the fermentative power of the yeast.
If a yeast with a very high fermentative activity is sought, it is necessary to apply higher hourly multiplication rates, and therefore higher O2 consumption rates and higher calorie production rates (rapid process). Consequently, the oxygen transfer and cooling capacities of the fermenter being what they are, it is necessary to reduce the amount of yeast in the fermenter and therefore to lose productivity.
One of the problems that the invention seeks to solve is therefore to provide at least one novel yeast strain having an improved fermentative activity compared with the reference strain I-2970 while at the same time being produced with a low mean multiplication rate (slow kinetics) and a productivity compatible with industrial and commercial use.
After multiple strain selection tests, the applicant has identified and selected a new strain which has an excellent fermentative activity while at the same time being produced by fermentation with slow growth kinetics, thereby making it possible to solve the problem mentioned above.